Electrolytic production of white lead



ELECTROLYTIC PRODUCTION OF WHITE LEAD Filed June 18, 1929 IHIIF1 In Ve a 1. 07":

Patented May" 10, 1932 UNITED STATES PATENT OFFICE ELECTROLYTIC PRODUCTION OF WHITE LEAD Application filed June "18, 1929, Serial No. 371,940, and in Australia July 6, 1928.

trodes to the action of direct current while immersed in a dilute aqueous solution of commercial sodium bicarbonate as an electrolyte.

The anode forms spongy 01' finely divided lead with carbonic acid gas and oxygen, resulting in the direct production of hydrated carbonate of lead, and the action of the cathode at which sodium and hydrogen are first released, results in the formation of sodium hydroxide and free hydrogen. As the anode becomes more or less inert, the polarity of the direct current is reversed, whereupon the cathode becomes an anode and the latter a cathode and the reverse operation occurs.

In practical operation the sodium bicarbonate solution is circulated through the electrolytic tank and with the gases from the electrodes, floats, or causes the hydrated carbonate of lead to rise in the tank, permitting ready flow to filter or a hydroextractor for deposition or separation of the very finely divided solid hydrated carbonate of lead.

To regenerate the depleted electrolyte (dilute aqueous solution of sodium bicarbonate) carbonic acid gas is fed into the liquid which reacts with the sodium hydroxide to form carbonate.

The accompanying drawing illustrates a diagrammatic lay out of a plant for carrying out the process continuously.

The electrolytic cells 3 contain the anodes and cathodes 4 which are electrically connected as shown to a source of direct current supply through a double pole changing switch 5 actuated at predetermined intervals.

by any suitable means as for example the liquid tilting device at 6 which controls the circuit of a solenoid 7 which controls an armature element 8 on said switch 5.

The electrolyte is circulated by pump 9 which elevates to tank 10 containing carbonic acid gas for regenerating the electrolyte, thence via pipe 11 to manifold 12, each branch 13 of the latter feeding to each cell. The overflow from each cell proceeds via overflow pipe 14 to conduit 15 to bottom tank 16, thence through filters or hydroextractor indicated at 25 back to pump 9.

The liquor flow via pipe 11 may conveniently be used to actuate the beforementioned tilting device at 6 by means of a branch pipe 11 delivering to vessel 17 containing the overbalancing twin compartment receiver 18 mounted on axis 19, which latter also carries arm 20 coupled to extension 21 of a pivoted single pole switch arm 22.

In the full line position shown of said switch arm 22 the energizing circuit of the solenoid 7 is open and the pole changing switch 5 is consequently in the lowered position with the solenoid de-energized. When the compartment, in the tilting device 6, receiving liquid from the branch pipe 11*, has received a sufficient weight of liquid it will tilt and cause reversal of the position of the switch arm 22 to close the circuit of the solenoid 7 which will attract armature 8 and cause. pole changing switch to take up the dotted position with consequent reversal of a the polarity of the current flowing to the electrodes in the cells 3. The solenoid circuit will remain closed until the tilting device at 6 is againactuated when the full line position of the switches 22 and 5 will again result.

Direct current of approximately six volts is employed to cause electrolysis, and reversal of polarity of the electrodes may be arranged to occur about every fifteen minutes, varying however according to surface area of the plates and plant capacity. I

In an experimental plant continuously op- ,erated' by the applicant and producing approximately three tons of white lead per week, 32 cells are used containing electrodes, each having a surface area of eighteen square feet. The electric current used is at the rate A of approximately .002 ampere per square inch of electrode surface at six volts.

The electrolyte is an extremely dilute aqueous solution of sodium bicarbonate of 15 grammes to four gallons.

The pole changing is effected after each period of fifteen minutes.

The fine particles of metallic lead which fall from the anodes are collected periodically from the bottom of the cells and may be utilized for commercial purposes e. g. for the production of chrome yellow. This step is 5 however merely ancillary to the process of producing commercial white lead, but is mentioned to indicate that, apart from escape of free hydrogen and oxygen, the chemical elements present may practically all be re covered.

I claim The process of electrolytically manufacturing white lead, comprising immersing lead electrodes in an aqueous solution of sodium 5 bicarbonate of grams to four gallons, passing a direct current of a capacity of 0.002 amperes at 6 volts to one square inch of electrode surface through the electrolyte, and reversing the direction of current flow at about every fifteen minutes, the current being reversal automatically by the electrolyte during its circulation.

ROBERT JOHN FROST. 

